The present invention relates generally to a radiography device and, more particularly, to a radiography device having a grease bearing with a gallium shunt.
The X-ray tube has become essential in medical diagnostic imaging, medical therapy, and various medical testing and material analysis industries. Typical X-ray tubes are built with a rotating anode structure for the purpose of distributing the heat generated at the focal spot. The anode is rotated by an induction motor consisting of a cylindrical rotor built into a cantilevered axle that supports the disc-shaped anode target, and an iron stator structure with copper windings that surrounds the elongated neck of the X-ray tube that contains the rotor. The rotor of the rotating anode assembly being driven by the stator which surrounds the rotor of the anode assembly is at anodic potential while the stator is referenced electrically to the ground. The X-ray tube cathode provides a focused electron beam that is accelerated across the anode-to-cathode vacuum gap and produces X-rays upon impact with the anode.
The dissipation of heat generated in the production of X-rays has been a driving force in the development of X-ray tube design. Excessive heat can have a negative impact on the X-ray tube""s performance. In addition, heat disbursed within the X-ray tube can have a deleterious effect on the bearings and lubricants used to facilitate the rotation of the anode. Bearings can become excessively worn and damaged over time and thereby degrade performance. Lubricants may break down when exposed to excessive heat and are also known to produce an effect referred to as outgassing. When lubricants experience outgassing, they break down from their fluid form and produce vapors that may penetrate the seals of the bearing compartment and penetrate into the vacuum portion of the X-ray tube. Once the vacuum portion of the x-ray tube has been compromised in such a fashion, the performance of the x-ray tube may be seriously impacted.
One approach towards increasing dissipation of unwanted heat has been directed through increasing the rotational velocity of the anode. While increasing the anode""s rotational velocity can improve heat dissipation, it can also carry with it the effect of straining traditional bearing designs. As the rotational speed increases, torque can be transmitted through the bearings and may result in race rotation, chatter, and excessive noise generation. Thus, considerable design effort has been exerted towards bearing and lubricant designs that are capable of handling the increased velocity. Often these designs result in complex bearing designs or novel lubricants that can negatively impact the time and cost involved in X-ray tube design and manufacturing.
A second approach to increasing the heat dissipation of the X-ray tube has been to combine rotation of the anode with secondary heat transfer modes. One such secondary heat transfer arrangement utilizes liquid metal, such as gallium, to provide thermal communication between the rotating shaft and external heat sink elements. Alternately, liquid metal itself may be used in the form of a plane bearing such that heat is transferred away from the shaft through the bearing itself. Often, however, while these designs succeed in controlling the anode""s temperature, they often fail to protect the bearings themselves from such thermal energy. Thus, the bearings may be subjected to undesirable temperatures and suffer the aforementioned detrimental effects. In addition, when liquid metal is used as the bearing or lubricant itself, the liquid metal may be subjected to undue stresses and may experience similar failures to traditional bearings such as outgassing.
It would therefore be highly desirable to have an X-ray tube rotation bearing that benefited from the simplicity and effectiveness of traditional bearing designs while being afforded the thermal protection provided by liquid metal heat transfer arrangements. In addition, it would be desirable to have an X-ray tube rotation bearing design that protected the vacuum portion of the X-ray tube from effects such as outgasing.
It is, therefore, an object of the present invention to provide an x-ray tube with a reduced thermal flow from the anode through the bearings. It is a further object of the present invention to provide an X-ray tube with a reduced likelihood of outgasing penetrating the vacuum portion of the tube.
In accordance with the objects of the present invention, an X-ray tube is provided. The X-ray tube includes an anode mounted to a rotatable shaft. The shaft is positioned within a central bore of a stem. A bearing assembly is positioned between the stem and the rotatable shaft. At least one grease injection port provides grease lubricant to the bearing assembly. A liquid metal shunt is positioned between the anode and the bearing assembly and is in thermal communication with the rotatable shaft and the stem. Heat generated at the anode location can thereby pass through the liquid metal heat transfer component and into the stem prior to impacting the bearing assembly.
Other objects and advantages of the present invention will become apparent upon the following detailed description and appended claims, and upon reference to the accompanying drawings.